The closest relative of Canis lupus, commonly known as the gray wolf, is the domestic dog (Canis lupus familiaris). Domestic dogs are considered a subspecies of the gray wolf. This close relationship is supported by genetic studies, which show that dogs and wolves share a high degree of DNA similarity.
Wolves and dogs can interbreed, producing fertile offspring, which further confirms their close genetic relationship. The domestication of dogs from wolves is believed to have occurred thousands of years ago, with humans selectively breeding wolves for specific traits, leading to the wide variety of dog breeds we see today.
In summary, the domestic dog is the closest living relative of the gray wolf, sharing a common ancestor and a significant amount of genetic material.